This invention relates to contact lenses and particularly to bi-focal contact lenses.
By the term bi-focal contact lens is meant a contact lens in which different portions of the lens are designed to have differing indices of refraction.
The eyeglass type bi-focal lenses have many advantages since a person wearing such glasses may readily see distant as well as close objects without changing glasses. Such lenses are, therefore, very popular.
Contact lenses, which eliminate the need for eyeglasses, are, of course, also very popular. These lenses, which cover a portion of the eyeball of the wearer, sit in virtually direct contact with the cornea, separated therefrom by only a thin film of fluid which covers the eyeball. The rear faces of such contact lenses are ground to correspond approximately with the curved contour of the cornea portion of the eyeball, while the front faces thereof are curved so as to give the desired optical effect. Typical modern contact lenses cover an area somewhat smaller than the cornea of the eye but considerably larger than the pupil of the eye and are kept in close overlying relation thereto.
Contact lenses have a number of advantages, the principal one being the close contact with the eye and relatively fixed position in use relative to the optical axis of the eye, which naturally results in better vision than is the case where the lenses are held in frames and the eyes look through different portions thereof. In other words, in contact lenses, the line of sight more nearly follows the optical center of the lens. Another advantage of contact lenses is their desirability from a cosmetic stand point and their greater safety in use than ordinary eye glasses in, for example, sporting activities and the like. Consequently, in recent years, many persons have come to prefer contact lenses over the ordinary eyeglass. While some attempts have been made to provide bi-focal contact lenses, until now, no one has been able to provide a practical bi-focal contact lens.
The ordinary bi-focal eyeglass lens is of this latter type since the wearer of the eye glasses only wishes the higher index or more highly refractive lens portion to be near the bottom of the lens where the glance will be when reading or doing other fine work. Thus, ordinarily, a person wearing a bi-focal lens wishes to use the long range vision portion of the lens most of the time and the reading or closeup portion thereof only when he is looking down.
Unlike the case with ordinary eyeglasses, there is no satisfactory known method of properly positionig a bi-focal contact lens on the eye so that it will function both as a distance lens and as a close-up lens while providing satisfactory vision in each.
One such known bi-focal contact lens is described in U.S. Pat. No. 3,279,878. This lens has a portion thereof with differing refractive index, sometimes referred to as the bi-focal segment of the lens, located in one sector or portion of the lens away from the geometric center thereof.
Such contact lenses were found to have several disadvantages. One is that the relatively thicker lower edge or bottom portion thereof was continuously being contacted by the eyelid. During blinking, if any rotational movement has started, for any reason, each further contact with the eyelid tends to aggravate the condition and cause the lens to rotate further. The principal objection, however, is that since the lens is positioned generally concentric with the optical axis, thus providing good distance vision, closeup material had to be viewed through a lens portion i.e., bi-focal segment, which was off-center with respect to the optical axis of the cornea and thus resulted in a substantial reduction in acuity.
Other known bi-focal contact lenses have been developed, such as the lens according to U.S. Pat. No. 3,431,327, which use an embedded metal weight for weighting the high index portion of the lens so as to properly orient it at all times. While such a construction may rotationally orient a contact lens about its optical axis and in fact is specifically designed for that purpose, the contact lens remains seated with its far vision segment in centered position i.e., in alignment with the optical axis of the cornea, so that when the eyeball moves down to reading position the contact lens moves with it. Thus, as noted above, closeup vision for reading or the like will always be along a line of sight which diverges from the optical axis of the cornea since such closeup viewing will be through a bi-focal segment located below such optical axis.
Accordingly, it is an object of the present invention to provide a bi-focal contact lens which will permit normal unobstructed vision for distance viewing while permitting clear and unobstructed vision for reading and other close viewing.
It is another object of the present invention to provide a bi-focal contact lens which, as a result of its novel construction, permits the wearer, with a minimum of effort, to shift from distance vision to near vision and vice-versa.
It is still another object of the present invention to provide a bi-focal contact lens which does not have the disadvantages of the known bi-focal contact lenses.